Our invention relates generally to electric lamps and particularly to those suitable for use on motor vehicles as headlamps. Still more particularly, our invention has to do with a vehicle headlamp of the kind having an incandescent lamp bulb, featuring provisions for protecting the drivers of oncoming vehicles as well as pedestrians from glare.
Incandescent lamp bulbs have been used extensively as light sources of vehicle headlamps. Normally, incandescent bulbs for vehicular headlamp applications have an envelope of vitreous material containing a filament. The envelope is formed in one piece with a base portion through which extend a pair of lead wires connected to the filament within the envelope portion. As is well known, the base portion is formed by pinch sealing one end of the tubular envelope; indeed, the base portion is sometimes referred to as a pinch seal. Pinch sealing is a widely practiced, efficient way of hermetically closing one end of the tubular envelope and, at the same time, providing the base portion in one piece with the envelope portion.
However, this practice has presented an inconvenience that has heretofore been left not completely resolved, particularly in use of incandescent lamp bulbs of this type as light sources of vehicular headlamps. The pinch sealing of one end of the tubular envelope unavoidably creates a generally tapering part of indefinite external shape and wall thickness between the envelope portion and the base portion.
Suppose that this bulb is mounted in position in a lighting chamber defined by and between a generally concave or paraboloidal reflector and a cover lens secured thereto. The rays of light that have been emitted by the bulb filament and which have passed through the tubular envelope portion will be reflected by the reflector into rays parallel to the optical axis of the headlamp unit. Then the parallel light rays will be directed by the cover lens to provide a desired beam pattern.
The light rays that have traversed the indefinitely tapering part of the bulb, on the other hand, will be thereby variously refracted. Subsequently reflected by the reflector, such random light rays will propagate in various directions at angles to the optical axis. The cover lens is incapable of converging the random rays into the desired beam pattern. Of the random rays issuing from the cover lens, those angled upwardly provide a cause of glare, dazzling the drivers of oncoming vehicles.
Conventionally, with a view to the reduction of such random rays deviating from the beam pattern, the bulb has been mounted to the lamp body or to the reflector in such a manner as to minimize the amount of rays that hit the reflector after traveling through the indefinitely tapering part of the bulb. We object to this conventional practice, first because it is a makeshift measure incapable of thoroughly eliminating the glare causing rays. Second, it has imposed limitations upon the internal design of the headlamp, particularly with regard to how to mount the bulb to the lamp body or to the reflector.